This invention relates to fastener elements and methods of securing them to an underlying film web, and more particularly to flexible extruded rib and groove fastener elements for use on reclosable plastic bags and methods of securing such elements to the bag wall.
Plastic containers or bags which feature reclosable fasteners are well known and widely used by consumers and industry. Typically, opposing rib and groove fastener elements (also called male and female profiles) on the container are pressed together or pulled apart to seal or open the container. Because of the popularity of such reclosable plastic containers, a number of different manufacturing processes and apparatuses have been developed to manufacture them. A major consideration in almost all of these prior art manufacturing processes has been the manner in which the fastener elements are formed and adhered or attached to the container walls. Problems have existed in manufacturing, such as twisting or distortion of the fastener elements when applied to a film substrate, obtaining secure adherence of the fastener elements to the film substrate, or other problems which reduce manufacturing speed and efficiency or otherwise increase manufacturing costs.
One approach to the problem of securing the fastener elements to a film substrate has been to form both the film and fastener elements integrally utilizing a single blown film die. This is the approach taken by Naito, U.S. Pat. No. Re. 29,208, which forms a unitary tubular film with fastener elements. However, as pointed out by Behr, U.S. Pat. No. 3,848,035, such an integral extrusion process is extremely difficult to carry out. Another technique taught by Sutrina et al, U.S. Pat. No. 4,263,079, is to place a fastener die in very close relationship to a film extrusion die and coextrude both the fastener and film. Adhesion of the fastener to the film occurs before any significant cooling of either the film or fastener.
Other prior processes have utilized the heat from hot, freshly-extruded, fastener elements in combination with a preheated traveling film web to fuse the elements to the film. Examples of such processes include Uramoto, U.S. Pat. No. 3,780,781; Noguchi, U.S. Pat. Nos. 3,945,872 and 3,784,432; and Takahashi, U.S. Pat. No. 4,279,677. However, the joining together of separately formed film webs and fastener elements presents manufacturing problems in terms of maintaining the fastener elements in an upright position during the joinder with the web and obtaining secure joinder without entrapping air between the bases of the fastener elements and the film web. Entrapment of air may result in adhesive failure of the lamination of the fastener element to the film web.
In order to aid in maintaining fastener elements upright during joinder, many prior processes used elements with wide and/or extended bases. However, such wide and/or extended basis contributed to air entrapment problems during joinder of the fastener elements to the film web. In the context of a coextrusion process, the Sutrina '079 patent discussed above illustrates the adhesion and air entrapment problems which occur if the traveling film and/or extruded fasteners having extended bases are not carefully joined together.
Accordingly, the need exists in the art for fastener elements and which can be readily and reliably secured to an underlying traveling film web.